The management of body core temperature by convective treatment is known. Convective treatment devices operate by receiving and distributing a flow of pressurized, thermally-conditioned air, and then expelling the distributed air through a surface to provide a generalized bath of thermally-conditioned air over, along, or around a person. To date, the predominant use of convective treatment has been to warm persons. In this mode, a flow of warmed, pressurized air is provided to stabilize or raise the body core temperature of the person in order to amplify comfort or to achieve a clinical objective. One such clinical objective is prevention or alleviation of hypothermia, a condition in which the body core temperature is less than some normal temperature. Convective warming devices have proven themselves to be extremely useful and highly effective in the treatment of hypothermic patients.
There are circumstances under which it would be desirable to deploy a convective thermal device in order to cool rather than warm a person. Again, comfort might be an objective. It might also be desirable to use a convective treatment device to lower the body core temperature. A beneficial effect would be the treatment of hyperthermia, a condition in which the body core temperature is greater than some normal temperature. Hyperthermia may result from environmental heat stress or from illness. Otherwise normal individuals may suffer hyperthermia when their natural cooling mechanisms, such as sweat, are overwhelmed during heavy physical exertion in a hot environment. Heat stress disorders, categorized in ascending order of severity, include heat cramps, heat syncope, heat exhaustion and heat stroke. Normally, a person will voluntarily stop working well before the onset of heat exhaustion, but some persons, such as competitive athletes or military personnel, may push themselves beyond this limit.
Hyperthermia may also be caused by fever associated with illness. Such fevers may have many causes, including infection, tumor necrosis, thyroid storm, malignant hyperthermia or brain tumor. Brain injuries that cause hyperthermia usually involve the hypothalamus, and may be caused by tumors, stroke, head injury or ischemic brain injury due to cardiac arrest.
The physiological consequences of hyperthermia span a spectrum of severity with fluid and electrolyte imbalances, increased cellular metabolic rates, and cognitive impairment being at the low end. In the mid-spectrum, motor skill impairment, loss of consciousness and seizures occur. At the high end, an individual may suffer irreversible cellular injury, especially of the highly metabolic brain and liver cells, and then finally organ failure and death. Hyperthermia is thus a condition that, depending on its severity, may require immediate cooling treatment to return a person's body core temperature to normal.
Cooling treatment may also have other important uses. In some situations, induction of mild-to-moderate hypothermia may provide beneficial protection against injury. The protective benefit of hypothermia has been shown when the blood flow to all or part of the brain is interrupted. Brain ischemia due to an interruption of the blood flow may occur during cardiac arrest, surgery on the brain or open-heart surgery. Cooling the brain before or in some cases after these events occur seems to be protective, and can decrease the severity of the ultimate brain damage.
Because of their eager acceptance and wide deployment, it would be very beneficial and effective to be able to adapt convective thermal devices designed and deployed for warming to also be useful for cooling as the need arises.
In fact, there have been proposals for adapting convective treatment devices to perform cooling. Some involve compounding convective treatment instruments with evaporative mechanisms. In such designs, convection is provided in order to magnify the cooling effects of evaporation. See, for example, the following patents, all owned by the Assignee of this application: U.S. Pat. No. 6,402,775, “High Efficiency Cooling Pads, Mattresses, and Sleeves”; U.S. Pat. No. 6,354,099, “Cooling Devices with High Efficiency Cooling Features”; and U.S. Pat. No. 5,860,292, “Inflatable Thermal Blanket for Convectively Cooling a Body”.
One drawback of these adaptations is the need to deal with moisture applied to a body, which may violate certain clinical protocols. In other proposals, air is cooled by the same mechanism that warms and pressurizes it for delivery to a convective treatment device. These mechanisms are, in effect, reversible cycle heat pumps that may be operated to deliver pressurized air that may be heated or cooled, or delivered at an ambient temperature. However, such devices are expensive and require frequent maintenance.
Therefore, there is a need for a simple, inexpensive mechanism that can adapt a convective treatment device to convectively cool a person for enhancement of comfort or for clinical purposes. Preferably, the adaptive mechanism should not require the application of moisture to the person and should not increase the complexity and expense of convective treatment instruments and systems. What is required is an inexpensive adaptor that can be easily and conveniently used to enable a convective treatment device to cool a person rapidly and effectively. Such a device will expand and enhance the utility of convective treatment equipment already deployed for use in warming.